1. Field of the Invention
The present invention relates to a memory system that includes a nonvolatile semiconductor memory.
2. Description of the Related Art
Some personal computers (PC) employ a hard disk device as a secondary storage device. In such PCs, a technology is known for backing up data that has been stored in the hard disk device to prevent the data from becoming invalid because of some failure. For example, when act of changing data in the hard disk device is detected, a snapshot as a backup copy of the data before the change is taken and a log of changes made to the data is generated. Then, processing for taking a new snapshot, invalidating a log taken in the past before the new snapshot was taken, and generating a new log is repeated at every predetermined time, which is disclosed, for example, in US Patent Application Publication No. 2006/0224636. In case data becomes invalid due to some reason, the data can be restored by referring to the snapshot and the log.